The present invention relates to a method of producing a substrate for a semiconductor device, such as an SOI substrate and a substrate for a FET which has an MFS structure (metallic film/ferroelectric film/semiconductor layer structure), which is suitable for crystal growth of a semiconductor layer or a ferroelectric layer on a silicon substrate wherein an intevening amorphous insulation layer is formed. More particularly, the present invention relates to a method of forming a substrate for a semiconductor device in which a crystalline insulation layer may be grown with an intervening insulation layer which has an excellent insulation characteristic on a silicon substrate for the purpose of growing a semiconducting crystal layer, a ferroelectric crystal layer, etc., and to a method of manufacturing such a substrate.
In relation to an SOI substrate for growing a semiconducting crystal layer on an insulation layer, for instance, among known methods are a method which requires bonding two silicon substrate seating oxide films with each other and polishing one of the two substrates to thereby leave a thin semiconductor layer. Another method requires injecting oxygen or the like at a surface of a silicon substrate to a constant depth and then annealing so that an insulation layer is buried in a semiconductor substrate.
Meanwhile, in a semiconductor memory device using a ferroelectric layer, the ferroelectric layer is formed on a semiconductor layer or on a surface of an electrode metal such as platinum with an intervening insulation film. In an MFS structure in which a ferroelectric layer is formed on a semiconductor layer, an oxide film is formed between the ferroelectric layer and the semiconductor layer, thereby degrading a crystal quality or morphology, or an interface state density between the ferroelectric layer and the semiconductor layer becomes large. Where the ferroelectric layer is formed on an insulation film, it is not possible to grow a ferroelectric layer which has an excellent crystal quality on the insulation film which is amorphous.
As described above, during fabrication of a semiconductor device, while it is necessary to epitaxially grow a semiconductor layer or a crystalline ferroelectric layer on a semiconductor substrate through an insulation layer in some cases, since the insulation layer is amorphous, it is not possible to grow a crystalline layer directly on a surface of the insulation layer.
Further, in the method which requires polishing one of the bonded silicon layers for thinning the one silicon layer, it is extremely difficult to polish the silicon layer into a uniformly thin layer. Furthermore, polishing is laborious. Therefore, a quality crystalline surface is difficult to obtain. In the method which requires injecting oxygen at a surface layer portion of a semiconductor substrate, ion bombardment greatly degrades a surface of a semiconductor layer. Therefore, in this method a high quality crystalline surface is also difficult to obtain. As a result, a crystal layer which is formed on such a deteriorated crystalline surface has a deteriorated crystal quality.
On the other hand, the inventors of the present invention invented a method of epitaxially growing an YSZ thin film on a silicon substrate and presented the method to Shingaku Gihou (ED96-42, CPM96-27, May 1996). This method makes it possible to obtain a crystalline insulation layer on a silicon substrate and epitaxially grow a semiconductor layer or a ferroelectric layer on a surface of the YSZ. However, since a YSZ thin film which is formed on a silicon substrate is a crystalline metallic oxide film and hence migrates ions, electric insulation of the YSZ thin film is inferior to that of a silicon oxide film or a silicon nitride films. Therefore, the YSZ thin film slightly degrades electric characteristics.